gemstone

Opal (in Jewelry Setting)

Hydrated Silicon Dioxide (SiO2·nH2O)

Hardness: 5.5-6.5 on Mohs scale. Color: White base with iridescent play-of-color (rainbow flashes). Luster: Subvitreous to waxy. Structure: Amorphous (mineraloid consisting of microscopic silica spheres).

Hardness: 5
Color: White base with iridescent play-of-color (rainbow flashes)
Luster: Subvitreous to waxy

Identified July 23, 2026More gemstone →

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Physical properties

Formation & geological history

Formed when silica-rich water precipitates in low-temperature underground cavities and fractures within sedimentary or volcanic rocks. Common in places like Australia and Ethiopia.

Uses & applications

Extensively used in fine and fashion jewelry, such as rings, necklaces, and earrings, as a birthstone (October) and decorative gemstone.

Geological facts

Opals are non-crystalline mineraloids containing up to 20% water trapped within their silica sphere structure. The diffraction of light passing through these tiny spheres creates the gemstone's famous 'play-of-color'.

Field identification & locations

Identified by its characteristic flashes of spectral color (play-of-color) against a white, clear, or dark background. Usually cut into cabochons or small inlaid stones in band rings.

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Diamond and Gold Jewelry

Carbon (Diamond) / Au (Gold)

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Ammolite

Ammolite (Biogenic Aragonite with trace elements; fossils of Placenticeras meeki and Placenticeras intercalare)

mineral

Cubic Zirconia (simulant) or Diamond

ZrO2 (Cubic Zirconia) or C (Diamond)

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Red Jasper

Silicon Dioxide (SiO2) with Hematite inclusions

sedimentary

Cubic Zirconia (or possibly Diamond)

Zirconium dioxide (or Carbon)

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Faceted Gemstone

Unknown transparent mineral, possibly Diamond (C), Cubic Zirconia (ZrO2), Quartz (SiO2), or Glass

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